A dynamic model for assessing soil denitrification in large-scale natural wetlands driven by Earth Observations.

International audienceThe Wetland Soils Denitrification Model (WSDM) developed here for natural wetlands, is a physical based model that proposes: (i) the inclusion of soil moisture and temperature from satellite-based Earth Observations at diurnal temporal resolution and (ii) the distinction of soils under different wetland typologies (i.e., flooded forests, freshwater marshes, brackish wetlands, peatlands, and complex wetlands). Despite uncertainties involved, these two features are key to upscale nitrification/denitrification dynamics in natural wetlands at landscape, regional and global scales. In this study, the performance of WSDM was validated with soils in flooded forests and freshwater marshes in the central Amazonian floodplain. WSDM multiannual time series (2012–2019) show that climate anomalies intensify denitrification events. Flooded forests were identified with the highest annual denitrification rates. Annual denitrification and N2O emissions estimated in this study are in line with previous studies

Local stakeholder perception as a key component to improve mangrove management in Matang, Malaysia

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Call for a collaborative management at Matang Mangrove Forest Reserve, Malaysia: An assessment from local stakeholders’ view point

Effective management of a socio-ecological system (SES) requires a good understanding of: (i) ecosystem functionality, (ii) interactions between social and ecological units, and (iii) stakeholder perceptions and activities. Matang Mangrove Forest Reserve (MMFR) covering 40,200 ha in Peninsular Malaysia is under silvicultural management (with a 30-year forest rotation cycle) for charcoal and timber production since 1902. The aim of this study is to assess the perceptions of (select) local stakeholders on the ongoing mangrove management of MMFR. Earlier, Huge et al. (2016), using Q methodology, identified three main shared perceptions, called discourses: (1) Optimization- ‘keep up the good work, but keep improving’, (2) Change for the better- ‘ecotourism & participatory management for sustainability’, and (3) Continuity – ‘business as usual is the way to go’. The current study is a follow-up to Huge et al. (2016) and reports on a survey which assessed the degree of support of the local stakeholders towards those three management discourses. The core statements of each discourse were presented as questions and then ranked by the participants. Based on the findings of the survey, the local stakeholders were clustered into three main working categories: (i) charcoal and timber workers, (ii) fishermen and (iii) service providers. The interviews held with 114 stakeholders indicated that discourse (2) ‘change for the better’ is the most popular (supported by 72% of the participants) regardless of the stakeholders’ working category. This discourse voices the involvement of local people in decision making, adopts participatory management, and encourages diverse mangrove-based economic activities beyond mere charcoal and timber production. Single-use management (focusing only on maximising charcoal and timber yields) was perceived as not equitably benefiting all local stakeholders. The insights of this study can guide the managers of Matang Mangrove Forest Reserve to improve the sustainability and the local support base for the existing mangrove management regime, e.g. by promoting diverse livelihood options for the local stakeholders.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Crab community structure as ecological indicator of Matang mangrove forest in Malaysia

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Denitrification in wetlands: A review towards a quantification at global scale

International audienceResearch to understand the nitrogen cycle has been thriving. The production of reactive nitrogen by humans exceeds the removal capacity through denitrification of any natural ecosystem. The surplus of reactive nitrogen is also a significant pollutant that can shift biological diversity and distribution, promotes eutrophication in aquatic ecosystems, and affects human health. Denitrification is the microbial respiration in anoxic conditions and is the main process that removes definitively nitrates from the ecosystem by returning of reactive nitrogen (Nr) to the atmosphere as N 2 and N 2 O emissions. This process occurs in the oceans, aquatic ecosystems and temporary flooded terrestrial ecosystems. Wetlands ecosystems are rich in organic matter and they have regular anoxic soil conditions ideal for denitrification to occur. In the current paper, we provide a meta-analysis that aims at exploring how research around global nitrogen, de-nitrification and wetlands had evolved in the last fifty years. Back in the time, wetland ecosystems were seen as non-exploitable elements of the landscape, and now they are being integrated as providers of ecosystem services. A significant improvement of molecular biology techniques and genetic extraction have made the denitrification process fully understood allowing constructed wetlands to be more efficient and popular. Yet, large uncertainties remain concerning the dynamic quantification of the global denitrification capacity of natural wetland ecosystems. The contribution of the current investigation is to provide a way forward for reducing these uncertainties by the integration of satellite-based Earth Observation (EO) technology with parsimonious physical based models

G-SWAF a 10 years dataset of global water dynamics from L-Band microwave: from concept to applications

International audienceMonitoring of in-land waters has gained a big interest in the last decade due to the high stacks related to water resources and the increased availability of satellite-based Earth Observation (EO) data for the detection of water surfaces. L-band passive microwave while providing deca-Kilometric spatial resolution observations is able to monitor water surfaces at high temporal resolution (<3days) under dense vegetated areas globally. Here, we present the algorithms basis of the latest 10 years dataset of Global Surface WAter Fraction (G-SWAF) available at www.catds.fr (Al Bitar et al. 2020). G-SWAF is based on multi-angular and dual-pole observation from the Soil Moisture and Ocean Salinity satellite. Level3 Angle binned Horizontal (HH) and Vertical (VV) polarization, Top of Atmosphere (TOA) Brightness Temperatures (TB) (Al Bitar et al. 2017) at 32.5 to 52.5 incidence angles are used to retrieve the surface water fractions. The retrieval is based on minimizing the quadratic difference between the modeled and the observed TB. Surface emission for forest is considered from spatio-temporal observations while the TB for water surfaces is modeled using radiative transfer principals. We present the validation and comparison of the G-SWAF product against water surfaces from microwave (SWAMP, GIEMS), SAR (ALOS-PALSAR), optical (MODIS), and altimetry (Jason2, Sentinel-3) (Parrens et al. 2017, Fatra et al. 2020). Fusion of the SWAF data with digital elevation models (SRTM, MERIT) and optical data (GSW) provides enhanced 1km resolution surface water maps (SWAF-HR) (Parrens et al. 2020). Several applications are also illustrated showing the added value of the G-SWAF product. Namely, the forcing of hydrodynamic models (MGB,SWAT) in tropical basins, a first EO based quantification of denitrification in the Amazon river (Guilerne et al. 2020, Martinez, et al. 2020), the monitoring of the floods in the Congo River Basin (Fatras et al. 2020), In the last section, we show how the combination of the G-SWAF with altimetric data can provide monitoring of water volumes in densely vegetated areas in preparation of the SWOT mission

Managing mangrove forests from the sky: Forest inventory using field data and Unmanned Aerial Vehicle (UAV) imagery in the Matang Mangrove Forest Reserve, peninsular Malaysia

Retrieval of biophysical properties of mangrove vegetation (e.g. height and above ground biomass) has typically relied upon traditional forest inventory data collection methods. Recently, the availability of Unmanned Aerial Vehicles (UAV) with different types of sensors and capabilities has proliferated, opening the possibility to expand the methods to retrieve biophysical properties of vegetation. Focusing on the Matang Mangrove Forest Reserve (MMFR) in Perak Province, Malaysia, this study aimed to investigate the use of UAV imagery for retrieving structural information on mangroves. We focused on a structurally complex 90-year-old protective forest zone and a simpler 15-year-old productive forest zone that had been silviculturally managed for charcoal production. The UAV data were acquired in June 2016. In the productive zone, the median tree stand heights retrieved from the UAV and field data were, respectively, 13.7 m and 14 m (no significant difference, p-value =.375). In the protective zone, the median tree stand heights retrieved from the UAV and field data were, respectively, 25.8 and 16.5 m (significant difference, p-value =.0001) taking into account only the upper canopy. The above ground biomass (AGB) in the productive zone was estimated at 217 Mg ha−1 using UAV data and 238 Mg ha−1 using ground inventory data. In the protective zone, the AGB was estimated at 210 Mg ha−1 using UAV data and 143 Mg ha−1 using ground inventory data, taking into account only upper canopy trees in both estimations. These observations suggested that UAV data were most useful for retrieving canopy height and biomass from forests that were relatively homogeneous and with a single dominant layer. A set of guidelines for enabling the use of UAV data for local management is presented, including suggestions as to how to use these data in combination with field observations to support management activities. This approach would be applicable in other regions where mangroves occur, particularly as these are environments that are often remote, inaccessible or difficult to work in.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

G-SWAF a 10 years dataset of global water dynamics from L-Band microwave: from concept to applications

International audienceMonitoring of in-land waters has gained a big interest in the last decade due to the high stacks related to water resources and the increased availability of satellite-based Earth Observation (EO) data for the detection of water surfaces. L-band passive microwave while providing deca-Kilometric spatial resolution observations is able to monitor water surfaces at high temporal resolution (<3days) under dense vegetated areas globally. Here, we present the algorithms basis of the latest 10 years dataset of Global Surface WAter Fraction (G-SWAF) available at www.catds.fr (Al Bitar et al. 2020). G-SWAF is based on multi-angular and dual-pole observation from the Soil Moisture and Ocean Salinity satellite. Level3 Angle binned Horizontal (HH) and Vertical (VV) polarization, Top of Atmosphere (TOA) Brightness Temperatures (TB) (Al Bitar et al. 2017) at 32.5 to 52.5 incidence angles are used to retrieve the surface water fractions. The retrieval is based on minimizing the quadratic difference between the modeled and the observed TB. Surface emission for forest is considered from spatio-temporal observations while the TB for water surfaces is modeled using radiative transfer principals. We present the validation and comparison of the G-SWAF product against water surfaces from microwave (SWAMP, GIEMS), SAR (ALOS-PALSAR), optical (MODIS), and altimetry (Jason2, Sentinel-3) (Parrens et al. 2017, Fatra et al. 2020). Fusion of the SWAF data with digital elevation models (SRTM, MERIT) and optical data (GSW) provides enhanced 1km resolution surface water maps (SWAF-HR) (Parrens et al. 2020). Several applications are also illustrated showing the added value of the G-SWAF product. Namely, the forcing of hydrodynamic models (MGB,SWAT) in tropical basins, a first EO based quantification of denitrification in the Amazon river (Guilerne et al. 2020, Martinez, et al. 2020), the monitoring of the floods in the Congo River Basin (Fatras et al. 2020), In the last section, we show how the combination of the G-SWAF with altimetric data can provide monitoring of water volumes in densely vegetated areas in preparation of the SWOT mission

Assessing methane emissions and soil carbon stocks in the Camargue coastal wetlands: Management implications for climate change regulation

Coastal wetlands are crucial in climate change regulation due to their capacity to act as either sinks or sources of carbon, resulting from the balance between greenhouse gas (GHG) emissions, mainly methane (CH4), and soil carbon sequestration. Despite the paramount role of wetlands in climate regulation few studies investigate both aspects. The Camargue is one of the largest wetlands in Europe, yet the ways in which environmental and anthropic factors drive carbon dynamics remain poorly studied. We examined GHG emissions and soil organic carbon (SOC) stocks and accumulation rates in twelve representative wetlands, including two rice fields, to gain insights into the carbon dynamics and how it is influenced by hydrology and salinity. Mean CH4 rates ranged between – 87.0 and 131.0 mg m−2 h−1and the main drivers were water conductivity and redox, water table depth and soil temperature. High emission rates were restricted to freshwater conditions during summer flooding periods whereas they were low in wetlands subjected to summer drought and water conductivity higher than 10 mS cm−1. Nitrous oxide emissions were low, ranging from – 0.5 to 0.9 mg N2O m−2 h−1. The SOC stocks in the upper meter ranged from 17 to 90 Mg OC ha−1. Our research highlights the critical role of low-saline wetlands in carbon budgeting which potentially are large sources of CH4 but also contain the largest SOC stocks in the Camargue. Natural hydroperiods, involving summer drought, can maintain them as carbon sinks, but altered hydrology can transform them into sources. Artificial freshwater supply during summer leads to substantial CH4 emissions, offsetting their SOC accumulation rates. In conclusion, we advocate for readjusting the altered hydrology in marshes and for the search of management compromises to ensure the compatibility of economic and leisure activities with the preservation of the inherent climate-regulating capacity of coastal wetlands.This Project has been funded by Foundation TOTAL (grant number: 2021 0439 ) and Agence de l'Eau (grant number: C002504 ). We also wish to thank Fondation MAVA for support, Claude Vella (CEREGE) for his help in collecting sediment cores, Loïc Willm for map production and remote sensing driven surface area flooding computing, The Conservatoire du Littoral et des Rivages Lacustres, The Réserve Naturelle Nationale de Camargue, the Parc Naturel Régional de Camargue, and the Réserve Naturelle Régionale de la Tour du Valat for allowing access to the study sites and their support.info:eu-repo/semantics/publishedVersio